There are various ways of referring to sources. You can use according to:
According to Cohen (1988), a d of .50 or higher suggests a moderately large effect.
Another way is to use a verb such as suggest:
In fact, Bassetto (2004) suggests that a commitment to ignore the zero lower bound is sufficient to rule out the existence of self-fulfilling equilibria.
A third way is to use the author’s name with ʼs and a noun:
Kawara’s investigations supplement Derrida’s analysis of copyright, a structure that simultaneously checks and explodes the proper name’s schismatic tendency.
Referring to sources
Manchester University Academic Phrasebank
Reporting verbs for introducing authors
University of New England
Verbs for Referring to Sources
University of Toronto
Using verbs of reference
Academic Writing : A Handbook for International Students, by Stephen Bailey